A capacitive touch panel is a substrate on which transparent electrode patterns are coated. When a finger is closes to or contacts the touch panel, a coupling capacitor is formed between the finger and the transparent electrode patterns because the finger is a conductor and has static electricity. Meanwhile, electrical capacitance of the electrode positioned at a touch point on the touch panel will change, thus making voltage or current on the electrode change. And then by comparing the voltage difference between the electrode and adjacent electrodes, a position of the touch point can be calculated.
However, although the touch input by the fingers is convenient, it is obviously difficult to achieve the following requirements of depicting lines with various thicknesses on a touchscreen, or realizing touch recognition for fine locations by the fingers. Therefore, in order to increase the accuracy of the touch, a solution by using a stylus has been proposed. The principle of the conventional capacitive stylus is mostly to disposed conductive rubber or foam on an end of a metal tube of the stylus. Although it can achieve a more accurate input with respect to the finger input, the capacitive stylus can not show the lines with the various thicknesses on the screen corresponding to force that exerts to the stylus, still having the shortcoming for the usage.
Therefore, in order to realize pressure sensing of the pen tip, an electromagnetic stylus has been proposed. The conventional electromagnetic stylus interacts with an electromagnetic sensor board behind the touchscreen. When the electromagnetic stylus is close to the touchscreen, the electromagnetic sensor board behind the touchscreen will sense an electromagnetic signal emitted from the stylus so as to obtain x and y coordinates of the position of the stylus. In addition, the electromagnetic stylus is equipped with a longitudinal pressure sensor. When a user is writing with the stylus causing the pen tip to be given a force, the pressure is transmitted to the pressure sensor via a pen core. A change of the pressure leads to a variation in the electromagnetic signal emitted from the stylus, and thus the electromagnetic sensor board can appear various pressure-sensitive values according to the signal.
However, the above-mentioned solution for achieving the pressure sensing requires disposing the electromagnetic sensor board behind the touchscreen. It will significantly increase costs.